Thermostatic metal



Sept. 27, 1927. 1,643,809 (2. E. FRY

THERMOSTATIC METAL Filed May 31. 1921 $5 k awe 140 55; T ZY Patented Sept. 27, 1927.

UNITED STATES VLLYTON I. EDT,

PATENT OFFICE.

'I'HERMOSTATIG METAL.

Application fled Kay 81, 1921. Serial No. 478,808.

This invention is directed to the provision of a thermostatic metal or thermostatic couple which is superior to those heretofore commonly used, particularly with respect to the range of temperature over which the metal may be used, the amount of work which the metal may be made to perform and the accuracy of the indications obtained even though the metal be subjected to a wide range of temperature variations.

A common practice heretofore in the manufacture of thermostatic metals has been to employ a nickel-steel such as invar steel and brass as the metals from which the thermostatic cou le is made. Invar steel is a nickel steel aving a nickel content of about 36% and it is of special value in a thermostatic couple for the reason that its coeflicient of expansion with changes of 1 temperature is practically zero at low temperature ranges. Brass is used as the other metal of the couple because it has a relatively high coeflicient of expansion. Such a thermostatic couple, though widely used heretofore, is not suited for use in obtainin accurate results under conditions which su ject the metal to relatively high temperatures, for instance, temperatures runnin well above 400 F. Furthermore, the loa that may be imposed upon such a thermostatic strip, especially at relatively high temperatures, must be small since otherwise the accuracy of the indications given by the movements of the strip will be greatly impaired.

There are many uses for thermostatic metals under conditions such that the metal would be sub'ected to temperatures running up to 600 or even 800 F. or 900 F. Also, it is frequently desirable to have the thermostatic metal move a valve or damper or some other element which imposes a load upon the strip greater than could be borne under the same temperature conditions by the strips heretofore commonly used without substantial loss of accuracy.

When a thermostatic strip of the type hitherto usuall employed and containing brass as the hig expansion element is heated to a temperature in excess of 600 F., it assumes a curved configuration by reason of the diflerent expansion coefiicients of the two elements; and when the strip is allowed" to cool to its original temperature, it does not assume its original shape exactl and the difference between its original an final shape represents the loss of accuracsy.

This alteration in the original ape of the thermostatic couple is due to the effect of the high temperatures upon the molecular structure of the brass whereby its elastic characteristics are so altered that whenthe couple is cooled to its initial temerature, it takes a set slightly difi'erent rom its original one. This permanent set takes place, particularly when the tem erature variations run up relatively hig as for instance well over 400 F., under the stresses imposed by the unequal expansion of the two metals and b any working load which the couple may caused to carry, such as the movement of a damper or valve.

It has been found that the stresses along the boundar zone between the two elements of the coup e are truly enormous, making it highly desirable not only that the joint shall be extraordinarily tenacious but also that both metals shall have appropriate elastic properties to enable them to recover their original configuration when these enormous stresses are removed.

I have found that the elastic characteristics and properties of ordinary brass, particularly at temperatures above about 400 F., are such as to render this metal unsuitable for use as the hi h expansion element in thermostatic-coup es designed for use under the conditions and for t e purpose mentioned. Thus, brass, in contrad stinction to many other alloys, such as the alloy steels, does not present the same substantial recover from the combined effects of stress an high temperature. On the contrary, ordinary brass will take on a substantially permanent set or permanent change in its configuration, when subjected to these influences, the change being the more pronounced when the stress and temperature conditions are continued for a substantial period of time.

By using in place of the brass a high expansion coefiicient metal which at the same time possesses a much hi her resistance to permanentrlistortion un er the combined effects of stress and high temperature, a thermostatic couple is produced which is adapted for use under relatively high temperature conditions and when subjected to the stresses specified, and accurate indications may be obtained in response to temperature variations even when those variations run u relatively high. The metal should be suc that subjecting it to a high temperature, such for instance as a temperature well over 400 F., will not cause a flow of the metal or a molecular change, such that when cooled to its original temperature, it would take a set difl'erent from its original shape.

A good example of a metal which, like brass, has a relatively high expansion coefficient, and which, unlike brass, possesses a much higher resistance to ermanent distortion under the combined e ects of stress and temperature, is an alloy of nickel and copper havlng a co er content materially lower than that o brass. A nickel-copper alloy which is well adapted for this use is Monel metal, an allo containing approximately 66% to 68% o nickel and 26% to 29% of copper. It has a relatively high coefficient of expansion with changes of tem erature, its elastic limit is substantially hig er than that of brass, and its desirable property of resisting permanent distortion under the combined influence of stress and temperature is not materially atiected by changes of temperature running up to 600 F., or somewhat igher, or at least they are not affected to such extent as would materially impair the accuracy of indications obtained from a thermostatic strip having one of its elements made of that metal.

The invention is employedto the best advantage by makin a thermostatic strip from invar steel and M mel metal, the invar steel being employed for the reason which has led to its use heretofore, namely, its negligible expansion coefficient at ordinary temperature ran es, and Monel metal being used because of its relatively hi h expansion coeflicient and its characteristic of retainin able elastic roperties when su jected to temperature 0 anges extending over a relatively wide range.

The primary advantage incident to this combination of materials rather than that heretofore employed as above described, is that it may be used under conditions which subject it to changes of temperature running much higher. After being subjected to these relatively higher temperatures and then allowed to cool, the thermostatic metal returns to substantially its original condition so that the accuracy of the indications afforded by the metal is not materially affected by the high temperature conditions.

Furthermore it is permissible to impose a its desirgreater load upon a thermostatic strip made from this improved metal without a substantial sacrifice of accuracy, as for instance, by arranging the strip to operate a valve, damper or switch member or similar device. The new metal will operate with accuracy under more severe load conditions throughout the ranges of temperature commonly met with in the operation of thermostatic strips, but this capacity of the newmh metal is particularly pronounced when the variations of temperature to which the strip is subjected include relatively high temperatures. A

The accompanying drawing is a representation of the improved thermostatic metal. The drawing shows strips of invar steel and nickel-copper alloy fused together throughout their entire length in any suitable manner.

I claim 1. A thermostatic couple consisting of two elements having different coeflicients of expansion fused together, both elements consisting of alloys of nickel, and the element having the higher temperature coeflicient having the larger nickel content.

2. A thermostatic couple consisting of two elements fused together, one having a relatively low temperature coeflicient and being composed of a nickel-steel alloy, and the other having a relatively high temperature coetficient and being composed of a nickel alloy having a nickel content larger than that of the other element.

3. A thermostatic couple consisting of two elements having difi'erentcoeflicients of expansion fused together, the element having the lower coeflicient being a nickel-steel alloy and the other element consisting primarily of nickel.

4, A thermostatic couple consisting of two elements having different coeflicients of expansion fused together, both of said elements containing nickel and the element of higher coeflicient having the higher nickel content.

5. A thermostatic couple consisting of two elements fused together, said elements being made of metal having difl'erent coefiicients of expansion, the element of lower ooeflicient being a nickel alloy containing less than 45% of nickel and the element of higher coeflicientcontaining more than 45% of nickel. 6. A thermostatic couple consisting of two elements fused together, said elements being made of metal having difi'erent coeflicients of expansion, the element of lower coeflicient being a nickel-steel containing less than 45% of nickel and the elem'ent of higher coefiicient containing more than 45% of nickel.

7. A thermostatic couple in which the element of the couple having the lower ex ansion coeflicient is a nickel-steel allo an the element of the couple which has t e higher expansion coeflicient is composed of an alloy of a relatively large proportion of nickel and a relatively small substantially as descri ed.

8. A thermostatic couple in which the element which has the relatively low expansion coefiicient is a nickel-steel alloy and the element which has the relatively high coefficient is composed of an alloy of approxiroportion of copper,

mately 26% m 29% copper and 66% m in invar-steel and the other composed of Monel ll metal substantially as described.

In testimony whereof I aifix m si ature.

CLAYTON RY.

mately 26% to 29% copper and 66% to la 68% nickel, substantially as described.

elements fused together, one composed of 9. A thermostatic couple consisting of two elements fused together, one composed of invar-steel and the other composed of Monel 1' metal substantially as described.

In testimony whereof I afiix my signature.

CLAYTON E. FRY.

Certificate of Correction.

Patent No. 1,643,809.

CLAYTON E. FRY.

Granted September 27, 1927, to

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 3, line 8, claim 8, after the Word high insert the word em amion; same and claim, line 12, strike out the words elements fused toget er, one composed of; and that thesaid Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 18th day of October, A. D. 1927.

[smart] M. J. MOORE, Acting of Patents.

Certificate of Correction.

Patent No. 1,643,809. Granted September 27, 1927, to

CLAYTON E. FRY.

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Rage 3, line 8, claim 8 after the word high insert the word expansion; same page, and claim, line 12, strike out, the words elements fused together, one composed of and that thesaid Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of October, A. D. 1927.

[SEAL] M. J. MOORE,

Acting Omnissiovwr of Patents. 

